Meters are widely used to measure the volumetric flow of commodities—particularly those provided by utilities, such as water, natural gas, and electricity. As one example, utilities typically interpose a meter into a conduit (e.g., pipe or wire) supplying a commodity to a residential or commercial end user. The meter includes some transducer operative to sense the volumetric flow of the commodity, and a register operative to maintain metered quantity data, such as a cumulative count of volume units of the commodity that have flowed through the meter. The count is periodically read, and by maintaining a record of at least the most immediate prior reading, interim usage or consumption of the commodity may be ascertained, and used for billing purposes, usage analysis, and the like.
Manually reading commodity usage meters is labor-intensive, time-consuming, and error-prone. Hence, a variety of electronic commodity usage meters is known in the art. For example, the register in many modern commodity usage meters houses electronic circuits that maintain the metered quantity data. The metered quantity data may be read from a register by a reading device applied to each meter, such as via electrical contacts or inductive coupling. Alternatively, a register may include an electrical, optical, or RF interface, connecting it to a communication network (e.g., LAN, WAN, cellular network, or the like), via which the register may be remotely interrogated, or may periodically transmit its identification and metered quantity data.
Electronic circuits in the register of a commodity usage meter require a power source. In many applications, a power source is not available, or would be expensive to install or extend to the meter, particularly given the limited functionality of the register and the relatively small amount of power required. In such applications, batteries may be sufficient to power the register of a commodity usage meter. However, batteries have a limited lifetime, their performance may vary with environmental factors such as temperature, and they require periodic recharge and/or replacement. Hence, an alternative, inexpensive power source for the register of a commodity usage meter, which requires no maintenance or replacement, would be advantageous.
A commodity usage meter is only active when the metered commodity flows—that is, when the commodity (e.g., water) is being consumed by the end user. In many cases, the meter spends the vast majority of its time in an inactive state. During such times, electronic circuits in the register may be placed in an inactive, low-power state, known in the electronic arts as “sleep mode,” to conserve power. Even when the meter, and hence electronic circuits in the register, is active, the register's fundamental function of processing a signal from a transducer in the meter, to update and maintain metered quantity data, does not require extensive consumption of power. For example, it may comprise simply detecting pulses from a sensor and incrementing a counter. In these cases, the greatest power demand of the register may be during a communication session with a reading device—that is, the operation of transmitting the accumulated metered quantity data out of the register. Accordingly, power source that is necessarily available during a metered quantity data communication session would be particularly advantageous.